Apparatus for lapping toothed elements



1939- I H. L. BARTER 2,165,329

APPARATUS FOR LAPPING TOOTHED ELEMENTS Filed Apr-i115, 1935 I 2 Sheets-Sheet 1 July 11, 1939. H. L. BARTER A PPARATUS FOR LAPPING TOOTHED ELEIENTS Filed April 15, 1955 2 Sheets-Sheet 2 m woiz w wgz M such as gears and the like and is more particu- Patented July 11, 1939 UNITED STATES PATENT OFFICE APPARATUS FOR LAPPING TOO'I'HE ELEMENTS Barry Lee Barter, Detroit, Mich., auignor to Packard Motor Car Company, Detroit, Mich, a corporation of Michigan Application April 15 1935, Serial No. 16,476

10 Claims.

This invention relates to apparatus of treating and finishing radially toothed machine elements larly concerned with the lapping or grinding of gear teeth after the formation of the teeth by the usual milling or cutting operations.

Itis common practice in the art to which this invention relates to improve the meshing of toothed gears by a lapping operation which involves engaging the gears with a lap member having corresponding teeth, and effecting relative reciprocation between the gear and the lap member, a suitable abrasive being supplied to' the cooperating toothed surfaces. For example, an externally toothed .gear and an internally toothed hardened lap, the latter having teeth aflording therebetween recesses within which the gear teeth may be received snugly or with a slight clearance, are relatively reciprocated in an axial direction, means being provided to simultaneously urge one of the cooperating members to.

rotate with respect to the other to apply slight circumferential pressure between the cooperating teeth. In practicing such a methodit is obvious that the gear and lap must be initially centered or aligned with the axes thereof in substantial coincidence and that this alignment must be maintained throughout the lapping operation in order that substantially the same circumferential pressure may be applied between each tooth of the gear and the corresponding teeth of the lap.

It is the principal object of the present invention to facilitate the initial aligning of the gear and lap and to provide an improved means for establishing and maintaining proper alignment thereof. By proceeding in accordance with the present invention the time and effort required for the substitution of one lap for another are greatly reduced, greater accuracy of alignment between the gear and lap may be attained, and the cost of manufacturing the lap is very materially lessened.

Further objects and features of the invention will be apparent from the following description taken in connection with the accompanying drawings, in which Figure 1 is a front elevation, partly in section, of one form of lapping machine to which the invention may be applied;

Figure 2 is a view in perspective of the lower end of the machine showing the parts assembled and in readiness for the lapping operation;

Figure 3 is a vertical sectional view of a supporting means for the lap and illustrates the preferred method of centering or aligning the l I Figure 4 is a plan view of the arrangement shown in Figure 3; and

Figure 5 is a sectional view on the line 5-4 6 j of Figure 1.

In order to facilitate-an understanding of the invention, a simple embodiment thereof is shown in the drawings and detailed language is employed in describing the several elements-of this em 10 the gear is worked-remaining stationary. -0b- 20 viously this arrangement may be reversed; axial reciprocation being applied to the lap while the gear is retained against displacement, and various other changes may be made in the details of con-- struction of the machine, these details constitut- 25 ing by themselves no essential part of the invention and being shown merely to illustrate the general nature of the machineto which the invention is applied. 7

The frame of the machine comprises a base 30 I0 and a head portion ll overlying the base, the head portion being supported by a standard l2 rising from the base. A shaft It, provided at its lower end with a reduced portion arranged to receive a gear II to be lapped, the latter being 35 secured in position by means of a nut I! or .in

any other conventional manner, is clamped or otherwise secured in a bracket 20. The bracket 20 may be generally U-shaped in horizontal section and is provided with a seat receiving a flange 40 2| at the upper end of the shaft Ii, the flange being introduced laterally on the seat and being retained in position by a clamping device which includes a member 23 pivoted on an eccentric portion of a shaft 24 which extends transversely of and is journalled in the bracket 20. A handle 25 is secured to the shaft 24 to rotate the latter, and the member 23 is provided at its lower end with an adjustable abutment 26 which, when forced downwardly by rotation of the handle 25, serves to clamp the flange 2| in position in the bracket 20. When the handle 25 is rotated in the opposite direction to raise the member 23, the latter may be swung outwardly and upwardly 55 about the shaft 24 to facilitate removal of the shaft l5 from the bracket.

The bracket 20 is secured at its upper end to a shaft 30, the shaft 30 being in turn carried at its upper end by a pitman 3|. The pitman 3| is journalled on a crank or eccentric portion 34 of a transverse shaft which is suitably journalled in the head portion of the frame and which is rotated by means of a pulley 38 secured to the shaft and driven through a belt 89 from a source of motive power.

The shaft 30 is suitably supported and guided for vertical reciprocation in response to rotation of the pulley 38, for instance by one or more bearings 40 carried by the head portion of the frame, and by a guide means of which the principal function is to ensure proper control of the shaft to enable the teeth of the gear to follow the teeth of the lap. For instance, if the gear and lap have straight teeth, it is desirable to prevent rotation of the shaft 30 during reciprocation thereof, whereas if the gear and lap have twisted or helical teeth, or are of some other configuration, the shaft should be rotated accordingly on its own axis during reciprocation.

Various devices may be employed for this purpose, but in the preferred form of the invention the guide means comprises one or more cooperating tongue and groove elements, such elements constituting in effect a cam device in the event the teeth of the gear and lap are not straight. Thus the shaft 30 may be provided with 'an enlarged portion having generally axially directed teeth 43 thereon, these teeth cooperating with corresponding internal teeth on a sleeve 46 which surrounds the shaft 30. Since the invention is illustrated as applied to the lapping of a helically toothed gear, the teeth 43 are constructed to afford a corresponding helix angle, it being understood that in the event a gear having straight teeth is being lapped, the teeth 43 will be correspondingly straight.

The lower end of the sleeve 46 may be provided with a toothed portion "with which a worm 48 is arranged to mesh, the worm being formed on shaft 49 to which a hand wheel 50 may be secured. It will be observed that unless the hand wheel 50 is rotated, the shaft 30 will be guided in a manner determined by the nature of the teeth on the gear I! and the cooperating lap; in the arrangement illustrated in the drawings and as the result of the employment of hell-- cal teeth on the shaft 30, the latter will be oscillated during reciprocation to impart corresponding movement to the gear H, the sleeve 46 remaining stationary, a rotatable coupling 53 of any conventional type being interposed between the crank and pitman and the shaft 30 to permit free rotation ofthe shaft.

If, however, the hand wheel 50 is rotated, torque will be applied to the shaft 30 through the toothed connection between the shaft and the sleeve 46, and pressure may thus be applied between one side or the other of the teeth of the gear I! and the corresponding teeth of the lap. In this manner opposite sides of the teeth of the gear may be lapped, it being understood that a suitable abrasive is supplied between the cooperating working faces of the teeth, and that the operation is continued until the gear teeth are ground into conformity with the lap teeth, irregularities developed during the cutting of the gear are removed, and an accurate and uniform contour of the gear teeth is secured.

It is sometimes desirable to index the gear greases with respect to the lap to promote uniformity, and it will be appreciated that the indexing can be readily eflected by operation of the handle 25 to release the shaft IS, the latter being raised to disengage the gear from the lap, rotated to a new position of alignment with respect to the lap, and again lowered and clamped in position.

As hereinbefore stated, the details of the construction thus far described form no essential part of the present invention and any other type of machine which provides for relative axial movement of the gear and the lap may be substituted for that illustrated herein. It is preferred, however, that the relative thiclmess of the gear and lap as measured axially and the range and stroke of the reciprocatory movement thereof be such that the gear teeth will extend beyond the opposite ends of the lap teeth at either extremity of the reciprocal stroke.

It is customary in order to achieve economical production to cast and chill the laps, and it has heretofore been the practice to grind the periphery of the lap to a true cylindrical contour in precise concentricity with the axis of the toothed portion of the lap, grinding of the upper and lower surfaces of the lap being also frequently resorted to. This has been necessary in order that the lap might be properly centered with respect to the gear to be ground by seating the lap in a support or receptacle having generally cylindrical or parti-cylindrical inwardly facing walls arranged to flt snugly to the corresponding cylindrical periphery of the lap. However, it will be obviousthat regardless of the degree of hardness of the lap, occasional replacement is necessary as the result of wear, it having been found that on an average only about sixty gears can be lapped before a new lap is required. When the old lap is removed and the new one inserted in accordance with the practice previously followed, the oil and abrasive commonly supplied to the lap and gear tended to collect on the cylindrical surfaces of the support and at other points in the pocket in which the lap is received, and it is found exceedingly difflcult to remove this oil and abrasive, the insertion of the lap involving a considerable loss of time for this reason.

Again, it is impossible by reason of the fact that the lap is chilled to employ a cutting tool on the periphery of the lap, and grinding of the lap periphery to the extreme accuracy necessary for correct alignment of the lap and gear is an expensive and delicate operation increasing to a very considerable extent the cost of the lap. It is found in practice that where the casting of the lap is inaccurately performed so that the lap periphery varies by as little as one-sixteenth of an inch from a truly cylindrical surface, the

grinding operation is so expensive as to warrant the rejection of the cast lap, this procedure resulting in the scrapping of about one-half of all of the laps cast.

By employment of the present apparatus none of the laps need be rejected, the grinding operation is wholly eliminated, and the lap may be inserted with the expenditure of a minimum of effort and time by the operator. The term unground lap is used herein to refer to a lap which is not. peripherally finished to that degree of accurate concentricity with the axis of its toothed portion to permit exact alignment and centering thereof by dependence upon such degree of accuracy of peripheral finish.

In the preferred form of the invention the lap support comprises a member 56 informed integrally with or secured to the base 10 of themachine frame and provided with a truly cylindrical or parti-cylindrical inner surface 51 and an inwardly directed annular flange 58. A member 60 having at its upper end an outwardly directed annular flange 62 may be received on the flange 58 of the member 56 as shown in Figure 3 of the drawings, the member 60 serving as a catch basin to receive the abrasive and the particles of metal ground from the teeth of the gear and lap. Seated on the fiange 62 of the member 60 is an annular member 65 having an outer cylindrical or parti-cylindrical surface 66 engaging the cylindrical surface 51 of the supporting member 56. The annular member 65 may be provided with a plurality of inwardly directed projections 68, three of these projections being shown in the drawings, each projection being preferably machined or ground on its upper surface to afford a seat for the lap ll.

A device is provided for accurately centering the lap with respect to the cylindrical surface 51 of the member 56, this device comprising a bracket I0 having one or more divergent legs 12 which are suitably strengthened and reinforced by ribs 13, the lower end of each leg being formed to provide parti-cylindrical surfaces 15 arranged to fit snugly within the cylindrical surface 51, the legs being adapted to rest on the annular member 65. The member 18 is further provided with a central sleeve portion 18 adapted to receive with a snug but sliding fit a shaft 19, the cylindrical surfaces 15 of the legs 12 being concentric with the axis of the sleeve portion 18. At its lower end the shaft 19 is provided with a reduced portion on which may be fitted an annular member 82 which is secured on the shaft by means of a nut 83. The annular member 82 has an accurately finished peripheral surface which is tapered slightly in an axial direction, the lower end of the member being slightly smaller in diameter. The upper end of the shaft 19 is provided with a handle portion 85 which may be grasped by the operator.

The bracket 10 is applied in position as. shown in Figure 3 of the drawings, the shaft 19 being first raised so that the member 82 is immediately above the lap. The shaft 19 and the member 82 are now lowered and the exterior surface of the member 82 engages the inner ends of the teeth on the lap and displaces the latter to a precisely concentric position, the weight of the shaft 19 and the member 82 being normally suflicient toaccurately center the lap.

Any conventional means may be provided for clamping the lap in the aligned and concentric position. The means shown in the drawings f r this purpose comprises a plurality of radlal clamping elements 86 which are arranged to rest on abutments 81 formed on the upper face of the member 65, these abutments serving as fulcrums for the elements 86. Bolts 90 extending upwardly from the member 65 pass through corresponding apertures in the several clampingelements and nuts 9| may be threaded on the bolts to clamp the inner ends of the elements 86 in engagement with the upper surface of the lap I.

When the lap H has been securely clamped in position, the bracket 10 may be removed and the machine prepared for operation in the conventional manner by insertion of the shaft I 5 and the gear l1 carried thereby in the bracket 20 as hereinbefore explained. Since the cylindrical surface 66 of the member 56 is accurately machined to alignment with the upper reciprocating parts of the machine, accurate alignment of the gear and lap is ensured. It will further be observed that since the cylindrical surface 66 is spaced to a considerable extent from the lap and gear, there is little possibility that abrasive, oil,

and dirt will collect on this surface, and consethe gear and lap, and means acting between said supporting means and said lap to secure said lap in axially aligned relation with the gear and against lateral displacement.

2. In a machine for lapping externally toothed gears, the combination with an internally toothed lap having an unground periphery, of means for supporting the lap and a gear concentrically for relative axial reciprocation with the teeth thereof in abrasive relation, said means supporting said lap 'for adjustment laterally of the axis of reciprocation to axially align the gear and lap, and means for frictionally clamping said lap on said support in axially aligned relation with the gear and against lateral displacement.

3. In a machine for lapping externally toothed gears, the combination with an internally toothed lap having an unground periphery, of means for supporting the lap and a gear concentrically for relative axial reciprocation with the teeth thereof in abrasive relation, said means supporting said lap for adjustment laterally of the axis of reciprocation to axially align the gear and lap, and means acting between said supporting means and said lap to secure said lap in axially aligned relation with the gear andagainst lateral displacement.

4. A device for centering a toothed gear lap on a support, said device having a portion arranged for engagement with the support at points lying outward of the periphery of said lap and a portion arranged for engagement with the toothed portion of the lap.

5. A device for centering an internally toothed gear lap on a support, said device having a portion for engagement with the support at points lying outward of the periphery of said lap and a portion displaceable axially of the lap with respect to said first portion for engaging the toothed portion of the lap.

6. A device for centering an internally toothed gear lap on a support, said device having a portion for engagement with the support at points lying outward of the periphery of said lap and a portion displaceable axially of the lap with respect to said first portion for engaging the ends of the lap teeth.

7. A device for centering an internally toothed gear lap on a support, said device having a portion for engagement with the support at points lying outward of the periphery of said lap and a portion displaceable axially of the lap with respect to said first portion for engaging the toothed portion of the lap, the displaceable portion of said device having a peripheral portion ofa diameter increasing in a direction axial of the lap.

8. A device for centering an internally toothed gear lap on a support, said device having a portion for engagement with the support at points lying outward of the periphery of said lap and a portion displaceable axially of the lap with respect to said first portion for engaging the toothed portion of the lap, the displaceable portion of said device having a generally cylindrical contour tapering in one direction from a diameter less than to a diameter greater than the diameter of the circle defined by the inner ends of the lap teeth.

9. In a gear lapping machine, the combination with a lap having internal teeth, and an unground periphery, of a member having a surface for engagement with one side of the lap, said member supporting said lap for displacement laterally of the lap axis, and devices for engaging the lap to clamp the lap against the said surface of said member.

10. In a gear lapping machine, the combination with a lap having internal teeth, and an unground periphery, of a member having a surface for engagement with one side of the lap, said member supporting said lap for displacement 1aterally of the lap axis, and devices for engaging the lap to clamp the lap against the said surface of said member, said devices constituting the sole means for retaining said lap against lateral displacement on said member.

HARRY LEE BARTER. 

